Usually Fold if you don't have a pair or better in the first 3 cards.
Remember the folded cards so that you know which cards are 'live'.
Play only live cards from the start and at least semi-live cards from the middle to the end.
Study your opponents. When he/she plays a low up-card, it is likely that the card is paired or just a loose starting hand of some sort. Does the player bluff? Can he or she be bluffed, etc?
Unless you are playing a strong draw hand, usually fold if your complete hand is beaten on the board by an opponent's up-cards.
Don't play for straights and flushes, except for 3 cards to a straight flush.
Usually don't play low hole cards.
Don't fall in love with your Ace in the hole. If that's all you have, against apparent strong hands, usually fold early.
Beware of the paired door card. This often means trips, especially if it is a low pair.
Get caught bluffing once in a while. It is a way to vary your play and not be too predictable. You win pots that you don't deserve when your bluff works. You lose a few chips when it doesn't work but it will get you calls from weaker hands down the line when you are strong and need the action.
Look for reasons to fold early. When someone else gets the card you wanted or you suspect that you are unprofitably chasing a better hand, fold it up. Trust your instincts and you will usually be right.